Integrated circuit (IC) packages traditionally include various metal layers interspersed with via structures forming what may be referred to as a metallization stack. This metallization stack provides power and other necessary electrical connections to underlying active devices such as transistors and the like. An emerging trend in microprocessor design is to bring additional functionality from the chipset onto the central processing unit (CPU) and this trend, along with other factors adding to the performance demand on the CPU, requires increasing numbers of signal connections on the die. This increase, along with decreasing die sizes, means that the technology is rapidly approaching a point where it will no longer be practical to place all of the signal connections around the perimeter of the die, and hence at least some of the signal connections must be placed in the middle of the die.
One way to form some of the required signal connections in the middle of the die would be to fabricate an additional thick metal layer in the metallization stack using the same process flow that is currently used for fabricating the existing thick metal layer in the metallization stack. This existing thick metal layer process flow is discussed in, for example, K. Mistry et al., A 45nm Logic Technology with High-k+ Metal Gate Transistors, Strained Silicon, 9 Cu Interconnect Layers, 193 nm Dry Patterning, and 100% Pb-free Packaging, Electron Devices Meeting 2007, IEDM 2007, IEEE International, 10-12 Dec. 2007, pp. 247-250. However, adding another thick metal layer using this process flow is unworkable for high volume manufacturing because of wafer bow issues and maximum process temperature restrictions for passivating the thick metallization layer.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements, while similar reference numerals may, but do not necessarily, denote similar elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.